1. Field of the Invention
The present invention relates to an antidissipation apparatus for evaporated fuel vapor.
2. Description of Related Art
One type of known antidissipation apparatus for evaporated fuel vapor used for preventing dissipation or emission of evaporated fuel vapor produced in a fuel tank to the atmosphere has been utilized by gasoline engines. Such antidissipation apparatus for evaporated fuel vapor has a canister to adsorb evaporated fuel vapor in the fuel tank, a purge passage to connect an intake manifold to the canister, and a purge control valve which is provided at the purge passage and opened or closed according to the driving condition of the engine. When the purge control valve is opened, evaporated fuel vapor which has been adsorbed by the canister is purged into the intake manifold by a negative pressure of the intake manifold and mixed to an air to be mixed to fuel. Thus, the dissipation of evaporated fuel vapor can be prevented.
The number of automobiles with lean-burn engines which utilize leaner than theoretical or economical fuel-to-air ratios in order to improve fuel consumption, is increasing. It is known that the leaner the fuel-to-air ratio becomes, the smaller the negative pressure of the intake manifold becomes. Since the negative pressure of the intake manifold is used to purge the evaporated fuel vapor into the intake manifold, it is difficult to purge the evaporated fuel vapor into the intake manifold when the engine becomes leaner.